Endoscopic ultrasound (EUS) procedures including endobronchial ultrasound (EBUS) procedures, as well as other endoscopy procedures (e.g., endoscopic retrograde cholangiopancreatography (ERCP) techniques used for viewing and treating the ducts that drain the liver and pancreas) provide advantageous, minimally-invasive means for diagnosis and treatment of many conditions. The body structures and passages that must be navigated with the scope-based devices present challenges for minimizing procedure times while maximizing efficacy of diagnostic and/or therapeutic procedures.
For example, with reference to gastrointestinal procedures, biliary ducts form a drainage routes into the duodenum from the liver and gallbladder and they join the pancreatic duct, just before they drain into the duodenum about 3 inches from the stomach. The drainage opening is called the papilla (Ampulla of Vater). The papilla is surrounded by a circular muscle, called the sphincter of Oddi. During ERCP, X-ray contrast dye may be injected into the bile duct, the pancreatic duct, or both via a catheter disposed through a working channel of an endoscope to aid fluoroscopic visualization of procedures. Those same systems may be accessed and visualized using EUS procedures, where use of ultrasound helps to reduce the amount of fluoroscopy exposure time spent by a patient and treating personnel.
A broad variety of techniques using ERCP and EUS (including in the gastrointestinal tract and elsewhere in patient bodies) have been and continue to be developed for minimally-invasive diagnosis and treatment of various conditions in a patient's gastrointestinal tract, and particularly in the structures of the biliary and pancreatic systems branching off from the duodenum. For a number of procedures using small gauge needles (often 19 ga. or smaller), the needle is introduced with a stylet disposed through the entire length or nearly the entire length of its longitudinal needle lumen. A standard bevel-tipped stylet 174 is shown in FIG. 1, including a proximal end cap 176 and a flexible elongate body 178. The stylet provides columnar strength while the needle is being directed to a target site, as well as minimizing the likelihood that an open distal tip and/or side aperture of, for example, a biopsy needle will collect tissue en route to the actual site being targeted.
In a biopsy procedure, the stylet will be removed from (or at least partially longitudinally retracted within) the needle lumen, typically after the needle is directed through an endoscope working channel so that its distal end is in or near the target site. As shown in FIG. 2, the endoscope (illustrated here as a duodenoscope 181, but readily understandable with application to an EUS scope) is directed down a patient's esophagus 191, then through the body, and up and around the pylorus of the stomach 193, then down/around into the duodenum 195. For the side-viewing camera and ports to properly orient relative to the sphincter of Oddi 197 and access the primary and branching ducts/passages of the biliary tree 199, the distal end portion of the endoscope 181 may be flexed/bent 90 degrees or more relative to longitudinal axis of the scope and to the already-curved scope body portion situated through the pylorus and duodenum, which is also shown. As such, the coaxial arrangement of a stylet within a biopsy needle assembly, oriented through an endoscope working channel is placed through a series of curves and turns between the proximal end accessed by an endoscopist and other treating personnel and the distal end (e.g., accessing the biliary tree), along and through all three axes of the patient's body.
It will be appreciated that this presents a relatively tortuous path for a needle disposed through the length of the endoscope 181. The same would be true for an EUS procedure, whether access is gained through a cannulated sphincter or by traversing a wall of the stomach, duodenum, or other structure. Thus, a stylet occupying the needle lumen may require significant force for withdrawal and removal (e.g., about 50 to about 100 Newtons), due to the binding friction between the outer surface of the stylet and the inner needle lumen surface along their respective lengths—and particularly along lengths where the scope is twisted and/or tightly curved. Stated differently, those of skill in the art will appreciate that certain points or lengths along the path of a stylet through a needle lumen may present greater frictional contact/binding force due to curvature of the needle (both on its own and relative to/interacting with an accessory channel of an endoscope through which it is disposed), causing an increased removal force required to remove the stylet from the needle lumen, as compared to a less curved, twisted, or otherwise distorted path. This higher level of removal force is inconvenient to the users, and it may have a negative impact on efficient workflow (e.g., by increasing the likelihood that the needle and/or scope is moved out of the desired position and/or orientation during stylet removal, by increasing procedure time, or other factors).
It may be desirable to provide a stylet and a stylet-needle system including a stylet structure that provides for reduced removal force without diminishing its other stylet functionality.